Why Toronto Should Become More Climate Change Resilient
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Why Toronto Should Become More Climate Change Resilient

Climate change is already well underway, but with some smart choices Toronto can mitigate the impact.

The future could get a whole lot hotter.

Imagine it’s 2040, and the daily temperature reaches a high of 44°C. This isn’t idle speculation—it’s what is projected for Toronto, according to a staff report [PDF].

But climate change isn’t just a threat that exists in the distant future. In reality, the effects of global warming are already plainly apparent across the Greater Toronto Area, and call for immediate action.

We need only look back to 2013 as a reminder that our typically moderate climate is not immune to the extreme weather associated with climate change: On July 8 of that year, a month’s worth of rain fell on the city in a matter of hours. Five months later, an ice storm rocked Toronto, leaving some residents without power for 12 days, and cost $106 million to clean up.

The impacts extreme weather like this has on the health of species and habitats, the city’s infrastructure, and watersheds are severe. Fortunately, the Toronto Region and Conservation, in conjunction with private partners and municipalities across the region, are working to stymie the effects of climate change. Here, we look at how the warming planet is taking a toll on the city, and what the TRCA is doing about it.


Plants and animals in urban settings face plenty of stress as is. Pressure from urbanization—reduced green space, rapidly growing human population, and chemical runoff into natural systems—can severely damage the diversity and health of habitats that thrived in pre-industrial times. For vulnerable populations, climate change is simply adding fuel to the fire. “Species that are already struggling may not have the adaptive resilience to take one more hit,” says Dena Lewis, manager of terrestrial and aquatic ecology at TRCA.

Take Toronto’s streams and rivers, for example, where salmonid species have been dwindling for decades, thanks largely to urbanization. Add to that rising water temperatures in Lake Ontario during spawning season—up 4.25°C since 1996—and these species are under considerable threat. “A lot of those species have fairly restrictive thermal regimes, says Lewis. “They can’t reproduce if the water temperature gets too warm.”

The TRCA has recently ramped up efforts to restore the region’s native Atlantic salmon populations by stocking the streams with hatchlings and building nurturing habitats to encourage their survival. The goal is that, one day, the species will spawn naturally and thrive in Toronto waterways, like they did some 200 years ago. The program is part of a larger initiative to improve aquatic diversity. “That’s what we do with all restoration efforts,” says Lewis, “try to ensure that the natural system we have in place is as diverse as we can make it, as resilient as we can make it.”

Indeed, low species diversity can have devastating effects in the face of climate change. Just look at Toronto’s urban forests, 50 per cent of which is populated by just four tree species. The forests have succumbed to several invasive species infestations in recent history, including the emerald ash borer, which is expected to wipe out all ash trees—10 per cent of Ontario’s forests—in a matter of a few years. While Lewis says it’s nearly impossible to know whether invasive species take hold because of climate change, “we know that many of these species take advantage of ecosystems that are stressed,” she says. “If your ecosystem is vulnerable for other reasons (like climate change) invasive species can take over quite easily.”

At this point, preventing extreme weather events is impossible, but tree planting efforts, coupled with policies to protect large trees in Toronto help maintain a resilient urban forest as climate change rears its head.


The built environment at once bears the brunt, and exacerbates the impacts, of extreme weather in the region. Milder winters and volatile freeze-thaw cycles mean roads and buildings wear down faster. At the same time, this infrastructure is a major threat to species, habitats, and the built environment itself, when coupled with extreme weather. Perhaps most damaging is that urbanization impairs the watershed’s natural hydrologic cycle: The natural system by which plants suck up rainwater and streams and rivers safely guide flood flows to the lake. When this hydrology is compromised and extreme weather hits, flooding is nearly inevitable.

Meanwhile, the concrete drainage channels built to compensate for the loss of natural drainage are proving inadequate against climate change. “The old pipes were designed based on old rainfall statistics, not our current or future climate,” says Glenn MacMillan, senior manager of water and energy with TRCA. Particularly in downtown Toronto, storm sewers are designed to withstand two-year storms—weather events that are 50 per cent likely to happen in a given year. “But those statistics are changing based on what we’re seeing in the weather,” says MacMillan. “There have been several 100-year storms in the last decade alone in Toronto.”

When rain exceeds the capacity of the sewer infrastructure, which it increasingly does, that water overflows, causing flooding and erosion that can damage roads, pipes, sewer systems, and buildings. One way to mitigate floods and damage to grey infrastructure is to establish more green infrastructure. Initiatives like the TRCA’s Sustainable Technologies Evaluation Program introduce things like green roofs, permeable pavements, and rainwater harvesting to properties across the city. “The principal of green infrastructure is to mimic waterflow before there was any development,” MacMillan explains. “It’s to reduce the amount of runoff and downstream problems by getting more of the water to infiltrate the grass.” And rainwater harvesting collects rain and uses it to flush toilets and irrigate crops. “We’re taking something that’s considered waste and treating it as a resource,” says MacMillan.

Watershed Management

On August 19, 2005, the biggest storm since Hurricane Hazel ravaged parts of the GTA. The three-hour rainfall triggered flash floods of creeks, rivers, and ravines. The damage—more than $600 million worth—included sewer backups, damage to pipes and roads, and severe erosion along water banks. The city was still grappling with the destruction when it endured an even bigger storm in July 2013.

Heavy downpours like these have lasting impacts on watersheds. They carry wastewater, fertilizers, and other pollutant into the rivers and streams, while eroding their banks and exacerbating flooding in the event of even moderate rainfalls. Meanwhile, warmer weather—another symptom of climate change—can lead to reduced base-flow water levels and more pathogens in Toronto’s waterways.

With more storms and droughts on the horizon, TRCA is striving to make watersheds more resilient. They’ve launched erosion control projects at Amberlea Creek, Ashbridges Bay, Fishleigh Drive, Gibraltar Point on Toronto Island, the Scarborough Bluffs, and the Don River. Along with restoring banks, these projects help reintroduce vegetation, create wetlands, and remove barriers to let fish swim up and downstream more easily. The most ambitious project on the docket is renaturalizing the mouth of the Don River. The southern portion of the Don was artificially straightened back in the 19th century in part to divert sewage and rainwater into the Ashbridge’s Bay Marsh. It only made flooding worse, however, and now the TRCA is working to reverse the damage with renewed greenspaces and trails to improve resilience across 290 hectares currently at risk of flooding.

That means safeguarding the area against Hurricane Hazel-sized storms, says Ken Dion, TRCA project manager and the organization’s lead on the Don River revitalization project. “Through computer based modeling we’re able to determine the volume and the extents of flooding that might occur under those scenarios,” he explains. From there, the coordinators tack on even more conservatism to plan for potentially bigger events.

“We’re really putting variability into the design to be able to accommodate future changes to the [ecology],” says Dion, noting that this preventative approach pervades all of TRCA’s restoration initiatives. “In our efforts now to address past issues and improve habitat structure, we’re also able to mitigate against the impacts of climate change as the weather becomes more volatile.”


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